The following information is provided to assist the reader to understand the invention disclosed below and the environment in which it will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the present invention or the background of the present invention. The disclosures of all references cited herein are incorporated by reference.
Medical imaging procedures often rely on the use of contrast media that is injected into the biological structure to be imaged such that the medical imaging procedure provides more detailed information to a radiologist or other medical personnel responsible for analyzing the medical imagery. Contrast media is often injected into a patient's vasculature prior to the medical imaging procedure and the patient's renal system is thereafter tasked with clearing the contrast media from the patient's bloodstream.
According to conventional radiographic diagnostic imaging techniques such as X-ray procedures, X-rays pass through a target object and expose an underlying photographic film. The developed film then provides an image of the radio-density pattern of the object. Less radio-dense areas produce a greater blackening of the film; more radio-dense, bony tissues produce a lighter image. Effective contrast media for X-ray may be either less radio-dense than body tissues or more radio-dense. The less radio-dense agents include air and other gases; an example of a more radio-dense contrast material is a barium sulfate suspension or iodinated injectable media.
Computed tomography (CT) is superior to conventional radiography in its ability to image, with extremely high resolution, a succession of thin sections of an object at specific points, lines, or planes along the X, Y, or Z axis of the target object. However, because this procedure is also based on the detection of differences in radio-density, requirements for contrast media in CT are essentially identical with those for conventional radiography.
Magnetic resonance imaging (MRI) systems for body imaging operate on a different physical principle. Generally, MRI relies on the atomic properties (nuclear resonance) of protons in tissues when they are scanned with radio frequency radiation. The protons in the tissue, which resonate at slightly different frequencies, produce a signal that a computer uses to tell one tissue from another. MRI provides detailed three-dimensional soft tissue images.
Fluoroscopy imaging systems may provide real-time X-ray images of internal structures based on differences in the radio-density of the imaged object components. As in X-ray procedures, fluoroscopy may be enhanced by the use of more radio-dense contrast media that may be injected into the object being imaged. For instance, in angiography procedures, radio-dense contrast media may be injected into the cardiac vasculature in order to trace the path of blood through the vasculature and determine, for instance, the location of blockages in the cardiac vasculature.
Currently, injection systems used for the dispensing of a contrast media in, for instance, CT, MRI, Ultrasound and/or Angiography/Fluoroscopy medical imaging procedures include interface controls and features limited to the delivery of contrast media within the medical imaging suite. Further, most contrast media is injected into a patient's vasculature for enhancement of imaging procedures and is then physiologically cleared by the renal system through normal nephritic function. During the clearing of contrast media from the patient's body, the serum-borne contrast media places additional burden on renal function until it is cleared. In cases where a patient undergoing a medical imaging procedure using contrast media has a prior history or an unknown pre-existing condition of compromised or impaired renal function, the burden associated with clearing injected contrast media can result in further damage to the kidneys and/or other components of the renal system. Furthermore, in some severe cases, the burden associated with the clearing of iodinated contrast media has destroyed renal function in its totality.
While contrast media used in imaging procedures is generally safe for healthy patients, there are cases of iodinated contrast induced nephropathy resulting from its use in medical imaging patients, as noted above. A representative medical imaging (and optionally treatment) procedure is generally a multistage or step procedure as generally depicted in FIG. 1. In FIG. 1, flowchart 100 illustrates an exemplary imaging procedure from a patient's perspective. In FIG. 1, a first step 110 includes obtaining detailed information concerning the patient such as name, medical history, insurance, next of kin information, etc. This information may be available directly from or confirmed by the patient or from a hospital information system (HIS). The imaging procedure may be conducted as an outpatient procedure or inpatient procedure. The patient is commonly informed about the procedure, discusses any concerns that they might have with the clinical personnel, and signs a consent form. The patient is then dressed appropriately for the procedure and commonly have an intravenous catheter inserted into his/her arm, and possibly is given some medication as preparation.
The patient preparation then continues in an imaging suite at step 120 where the patient is placed on the imaging table, typically given some moderate sedation, and further prepared for the procedure. In a catheterization lab, this step may include generally covering the patient with sterile drapes and preparing a sterile field commonly in the groin area for access to the femoral artery. Blood tests are commonly done to measure clotting time and medication is given to provide for the right level of anticoagulation. The attendant clinical personnel and technicians also prepare various medical devices and systems for use in the procedure, open packages of sterile products and put them onto a sterile table for ready access. Step 120 also includes gaining access to the femoral artery with a sheath, a guidewire, and then a catheter. The guidewire and catheter may be maneuvered some distance before contrast needs to be injected for visualization of their position relative to the patient's vasculature.
When a clinician needs to inject contrast, the contrast imaging phase begins at step 130. Modest “puffs” of contrast are often injected to help the clinician maneuver the catheter into the correct position. Once the catheter is in the correct position, a larger bolus of contrast is typically injected to allow visualization of the vascular tree and identification of any stenosis or other abnormalities of concern. If there is a stenosis or blockage, it can often be treated during the same procedure with angioplasty or insertion of a stent, which involves additional maneuvering of catheters and contrast injections. Once the treatment is competed, no more contrast is injected.
To complete the procedure in the imaging suite at step 140, the catheters are removed from the patient and the wound is closed with stitching of the tissue that had been cut and optionally, the vessel wall. Blood tests may be drawn to ensure that there is sufficient reversal of anticoagulation for the patient to be moved to a recovery area. After being sufficiently stabilized, the patient is wheeled out of the procedure room to the recovery area. The treatment outside the recovery room at step 150 commonly includes observation and monitoring while sedation wears off. Once the patient is coherent enough to understand medical instructions, the patient and any person accompanying the patient are given follow up instructions on wound treatment. The patient then dresses and is prepared for discharge.
The foregoing process can be considered to include three phases: a first or preparation phase 161, a second or injection phase 162, and a third or recovery phase 163. First or preparation phase 161 may be considered to include those steps needed to prepare the patient for a first injection of contrast, including those steps occurring outside and inside of the imaging suite (e.g., steps 110 and 120). Second or injection phase 162 may be considered to encompass the time of first contrast injection to the time of last contrast injection (e.g., step 130). Third or recovery phase 163 may be considered to encompass the time from last injection to a time long enough after the injection phase 162 that it is clear that there are no after effects from contrast injection (including, steps 140 and 150).
Contrast induced nephropathy (CIN) may be defined as a serious degradation of kidney function in patients who have received vascular injections of, for example, iodinated contrast medium. CIN occurs more frequently in patients with known risk factors such as previous administration of contrast, diabetes mellitus, congestive heart failure, obesity, and age-related factors. The condition is relatively rare (less than 5% of the total population receiving contrast), but it occurs with higher frequency (11-50%) and severity in patients whose renal function is already impaired. In more severe cases, CIN can result in the need for dialysis, and it can sometimes result in death. Often, CIN will not become apparent until at least 24-48 hours after contrast administration. This delay in manifestation complicates real-time assessment of kidney function at the time of contrast administration.
The standard of medical care to prevent as well as to treat CIN is “hydration therapy”, which includes the intravenous infusion of normal saline at a rate of at least 100 ml/hour for 4 to 6 hours before a contrast-enhanced procedure, followed by several additional hours of intravenous saline. Oral hydration is also recommended for patients at risk of CIN, as an adjunct to intravenous therapy. Fluid volumes between 1-2 liters are believed to stimulate renal excretion of contrast media along with all the additional water.
Although hydration therapy is the standard of medical care to prevent or to treat CIN, slow hydration therapy via intravenous infusion can sometimes result in an overage of fluid in the body, progressing to edema, pulmonary effusion, congestive heart failure, and a worsening of cardio-renal function. It is expected that balancing the urinary output with intravenously infused fluid can reduce the side effects of hydration therapy. A commercial device, RENALGUARD™ (available from PLC Medical Systems, Inc. of Franklin, Mass.) attempts to perform this balancing function over a period of time shorter than the 12-24 hours required by conventional hydration therapy. A drawback of the RENALGUARD™ device is the need to introduce a drainage catheter into the urinary bladder, resulting in patient discomfort and inconvenience for the operator.
Based on the results of clinical trials, CIN can be significantly reduced by intravenous infusion of sufficient fluid volume to promote a glomerular filtration rate (GFR) in excess of 150 ml/hr. (See, for example, Stevens, et al. “A Prospective Randomized Trial of Prevention Measures in Patients at High Risk for Contrast Nephropathy,” J of the ACC, Vol. 33. No. 2, 1999, pp. 403-411.) It is currently difficult to measure GFR because of the costs associated with extracting and analyzing blood samples with laboratory equipment (for example, using the RENALYZER™ analyzer available from Provalid AB Corporation of Aldernansgatan, Sweden). A somewhat more practical way to assess kidney function is to measure urine output over time. However, measurement of urine output also requires the use of a urinary catheter to collect kidney output.
In a post hoc analysis, Buckley, et al. showed that imaging of the kidney blood flow by means of dynamic contrast enhanced MRI (DCE-MRI) provided data that correlated well with reference measures of GFR. (Buckley, et al. “Measurement of single kidney function using dynamic contrast-enhanced MRI: comparison of two models in human subjects”, J Magi Reson Imaging, 2006 November; 24(5): 1117-23.) Further, Hackstein, et al. showed that total GFR can be measured with CT images of the abdominal aorta with minimally extended triphasic CT in patients without acute renal disorder by using a two-point Patlak plot technique. (Hackstein, et al., “Glomerular filtration rate measured by using triphasic helical CT with a two-point Patlak plot technique”, Radiology, 2004 January; 230(1):221-6.)
Given the significant health related problems which may result with contrast induced nephropathy, it is desirable to develop and implement devices, systems, and methods for predicting, preventing and/or mitigating the effects of contrast induced nephropathy. Accordingly, this disclosure is directed to devices, systems, and methods for mitigation of contrast induced nephropathy which may result from the administration of contrast media during medical diagnostic and/or therapeutic procedures such as those described hereinabove.